Choose Your Case and VRM Cooling Solution

Most X399 motherboards have VRMs like the ones pictured above. These motherboards don't have active cooling on their VRM heat sinks, but their VRM heat sinks are beefed up a lot and are designed to take advantage of environmental airflow inside a case. VRM overheating leads to CPU throttling, and it is one of the two most common reasons that Threadripper CPUs don't perform at their best at stock and especially when overclocked. The two VRM heat sinks pictured above do best with active airflow.

One vendor (left) went so far as to integrate a hidden fan that would help actively cool down the VRM, but as most of us know; smaller fans tend to be louder when moving more air. One vendor (right) actually includes mounting hardware so you can mount a fan directly above your CPU VRM, and that is the perfect solution for a system on a test bench.

Open air cases (such as the Thermal Take Core P5) and test benches (such as the Open BenchTable), as well as custom benches, are gaining a ton of traction because they put your hardware right in front of you where you can stare at it like a work of art. While these are glorious alternatives to a case, they can produce a huge issue; lack of active airflow over the motherboard area. Worse yet, with water cooling solutions, you don't get the same indirect airflow you might get with an air cooler.

Instead of talking about theoretical scenarios, I went ahead and actually tested out how much the system environment effects VRM heat sink temperatures. I taped a K-type probe to my Sper Scientific type-K/J thermometer which offers a very fast refresh rate and logging of maximums. For the case scenario, I tested two different air flow types; positive pressure (natural airflow pushing out of the case) and negative pressure (natural airflow pulling air into the case). I set up my Corsair 900D with seven fans, the three from the Enermax Liqtech at the top of the case exhaust hot air, and three fans at the front blow air into the case. The seventh fan is a high-pressure Enermax fan mounted at the rear of the case (you can see it in the image above), which I had blow into the case for the positive pressure test and blow out of the case for the negative pressure test.

I used the thermal probe temperatures, and the probe is touching the center of the heat sink of the motherboard pictured earlier, and doesn't move at all. I tested with no fan on a test bench, an active fan on the test bench (I used the VRM fan mount pictured earlier), negative pressure inside a closed case, and positive pressure inside a closed case. Results from VR1 and VR2 are the PWM controller's estimation of the VRM temperature (they are obviously on an offset as to not freak out the user) to make sure the trend I saw on the heat sink was correct. I found that the VR1/2 temperatures did follow the trend of temperature change that my thermal probe reported. The best way to cool down the VRM is obviously with a 120mm fan mounted above the VRM pointing right at it on the test bench, and the worst way to cool the VRM is to have no airflow on an open-air test bench/open case. However, the surprise is that there is a big difference between negative and positive case pressure inside a closed case.

With positive pressure inside the case, I found that thermal probe temperatures were actually very close to that of an active fan blowing at the VRM heat sink, and I found that with negative pressure things were much worse. All of this means you can get away more easily with a build inside a case that uses positive airflow (this is recommended by many in the industry as well). I recommend using one of your stronger fans mounted at the back/front of the case blowing in, as fans at the bottom that blow in might have their airflow obstructed by your GPU.

These results are just those of my specific setup, and they may differ for you, but it's possible to keep VRM temperatures down with solid case airflow. All said and done, you should purchase some quality fans that offer excellent airflow/air pressure/noise specifications.

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